Green Heron takes notice, takes flight

This Green Heron was quietly grooming itself when it suddenly went alert. It focused hard on something behind me. Then it left in a rush, flying not to a another tree or the adjacent marsh. It flew out of sight. What was its problem? A small flock of swallows, Barn and Tree mixed, swooped in to chase the heron for maybe 100 yards. They quit the chase. The heron kept going. Any large dark bird probably gets that treatment, seen as a possible threat to nests and baby birds. Crows and raptors certainly deserve that concern. Green Herons are innocent, however, birds and eggs not listed as part of their diets.